In case you don't have the capability to add marketing permission tagging to your website before or soon after GDPR becomes in effect on May 25th 2018, you can also upload your email lists to Nosto manually.
The tool will cross-reference the uploaded email list against Nosto's list of known and identified customers and will add marketing permission true for those individuals that are already in Nosto's database. Effectively the uploaded list of users might receive Triggered Emails from Nosto as they are treated as subscribers for your email marketing.
The tool supports approximately batches of 25.000 emails per upload.
In case you want to automate the process of updating the consent status, you can do so via API. You would request one from the support (pink bubble on the bottom right or firstname.lastname@example.org) and get the information on how to utilize it from our API documentation.